1. Field of the Invention
The present invention relates to a silicone rubber composition which, when cured, can provide vulcanized molded items excellent in heat resistance and fire retardancy and to its cured product.
2. Description of the Prior Art
Silicone rubbers are excellent in heat resistance in comparison with common organic rubbers such as butadiene rubber and isoprene rubber and are widely used in the application where heat resistance is required for example in fire-resisting gaskets and oil seals of motorcars.
It is known that by adding a phenyl-group-containing polysiloxane to a silicone component of a silicone rubber the silicone rubber is provided with refractoriness, fire resistance, and radioactivity resistance. It is also known that the properties such as the heat resistance and fire resistance are further improved by using as a dispersant a phenyl-group-containing polysilanol such as diphenylsilanediol and phenylmethylsilanediol.
Generally, when a phenyl-group-containing polysiloxane is used, it is required to use the above-mentioned phenyl-group-containing polysilanol as a dispersant in order to improve the compatibility.
Further, the phenyl-group-containing polysilanol as mentioned above has a defect that since it is solid at normal temperatures it does not function as a dispersant if it is not heated and it must be used in combination with other dispersant. In addition, diphenylsilanediol, phenylmethylsilanediol, and the like change to more stable cyclic compounds such as 1,1,3,3,5,5-hexaphenylcyclotrisiloxane and 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane under the conditions wherein an acid owing to a filler is present and therefore blooming occurs on the obtained vulcanized molded item.